This is a study of bone mineral structure and properties with emphasis on the elucidation of the biochemical processes of tissue mineralization. The term structure, as used here, includes the identification of the chemical phases in bone mineral, the atomic arrangement of these chemical constituents and the spatial and chemical relation between the mineral and the organic matrix of bone. Such techniques as x-ray diffraction and infrared absorption spectrophotometry will be used in this project. X-ray radial distribution function analysis of the diffraction patterns will be employed for determining the structure of the poorly crytallized, submicroscopic, biological apatites and their synthetic calcium phosphate analogues. The changes of mineral and organic constituents of calcified tissue as a function of time will be studied by separating various hard tissues into a series of density fractions (the lightest is the least mineralized tissue). In vitro studies of the effect of proteoglycan aggregates and proteoglycan subunits on apatite precipitation and growth will be continued.